A major effort is being made to extend the period of safe pacing of the diaphragm for chronic ventilatory support in patients, applying the information obtained from experience with a laboratory model. Stimulation parameters will be varied first in the experimental and then in patients to diminish as much as possible the current received by the phrenic nerve and still provide adequate ventilation. Such variations are (1) current level, (2) wave form, (3) pulse interval, (4) respiratory rate, and (5) electrode design. Additional clinical studies will include an analysis of the effectiveness of long-term (5 or more years) pacing for ventilatory support, analysis of the causes of upper airway obstruction in patients with chronic ventilatory insufficiency, and evaluation and management of respiratory complications accompanying pathologic lesions of the brain stem. Experimental studies will include evaluation of a total implant diaphragm pacemaker in vitro and in vivo, and a study of the effect of chronic stimulation on muscle metabolism.